diff --git a/packages/auth/src/di/bind-production.ts b/packages/auth/src/di/bind-production.ts
index 2af12a1..94d5868 100644
--- a/packages/auth/src/di/bind-production.ts
+++ b/packages/auth/src/di/bind-production.ts
@@ -6,6 +6,12 @@ import {
   type ILogger,
 } from "@repo/core-shared/instrumentation";
 import type { BindProductionContext } from "@repo/core-shared/di";
+import type { ProductionUseCase } from "@repo/core-shared/conformance";
+import type { AuthManifest } from "../feature.manifest";
+import type {
+  SignInInput,
+  SignInOutput,
+} from "../application/use-cases/sign-in.use-case";
 import { authContainer } from "./container";
 import { AUTH_SYMBOLS } from "./symbols";
 import { UsersRepository } from "../infrastructure/repositories/users.repository";
@@ -53,7 +59,11 @@ export function bindProductionAuth(ctx: BindProductionContext): void {
     .toConstantValue(authService);
 
   // Use cases — wrapped with span + capture at bind time
-  const wrappedSignIn = withSpan(
+  const wrappedSignIn: ProductionUseCase<
+    SignInInput,
+    SignInOutput,
+    AuthManifest["useCases"]["signIn"]
+  > = withSpan(
     tracer,
     { name: "auth.signIn", op: "use-case" },
     withCapture(
diff --git a/packages/core-shared/src/instrumentation/with-span.ts b/packages/core-shared/src/instrumentation/with-span.ts
index eeb6b09..0685b0c 100644
--- a/packages/core-shared/src/instrumentation/with-span.ts
+++ b/packages/core-shared/src/instrumentation/with-span.ts
@@ -1,6 +1,16 @@
 import type { ITracer, SpanOpts } from "./tracer.interface";
 import type { Instrumented } from "../conformance/brands";
 
+export function withSpan<Args extends unknown[], R, Extra extends object>(
+  tracer: ITracer,
+  opts: SpanOpts | ((args: Args) => SpanOpts),
+  fn: ((...args: Args) => Promise<R>) & Extra,
+): Instrumented<((...args: Args) => Promise<R>) & Extra>;
+export function withSpan<Args extends unknown[], R>(
+  tracer: ITracer,
+  opts: SpanOpts | ((args: Args) => SpanOpts),
+  fn: (...args: Args) => Promise<R>,
+): Instrumented<(...args: Args) => Promise<R>>;
 export function withSpan<Args extends unknown[], R>(
   tracer: ITracer,
   opts: SpanOpts | ((args: Args) => SpanOpts),